The Just War Theory was a developed theory as to what determined a just or morally right war.
The Just War Theory was written in the 16th to mid 17th century known as the “Classical Period”, and was developed by various philosophers throughout history, the majority of them being Christian philosophers.
In the document of The Just War Theory, the philosophers developed reasons that define a just war. For example, the Just War Theory states that a war can only be waged by a proper high authority, the war must be a last resort, chance of victory in a war must be likely, and civilian women and children should not be harmed. These are only a few examples mentioned in the theory, but the establishment of this document marked the beginning of a benchmark used for all future wars to come.
God’s law was applied and used throughout the Just War Theory, and served a great amount of influence in its development. The philosophical developments of Thomas Aquinas, Hugo Grotius, Augustine of Hippo, Aristotle, and others contributed to the search for what was just in war time. The theory would also be modified later after its first time being published for newly devised moral reasons affiliated with war.